Certain mobs cause log error spam in Mob Spawners

This is a re-report of MC-192362 after I was able to confirm the issue on a clean new vanilla install. No mods, default options, and new world.

Steps to reproduce:
1. Give yourself a mod spawner ( /give @p minecraft:spawner )
2. Place it and right-click the spawner with an enderman spawn egg

Expected result:
The spawner should display a small enderman rotating inside of it.

Actual Result:
The mob inside the spawner became invisible and errors like below began printing to the log repeatedly (full log attached).

[21:27:35] [Render thread/WARN]: Exception loading entity: 
s: Loading entity NBT
	at aom.f(SourceFile:1645) ~[1.16.1.jar:?]
	at aoq.a(SourceFile:468) ~[1.16.1.jar:?]
	at aoq$$Lambda$4119/615184896.accept(Unknown Source) ~[?:?]
	at v.a(SourceFile:401) ~[1.16.1.jar:?]
	at aoq.a(SourceFile:467) ~[1.16.1.jar:?]
	at aoq.b(SourceFile:530) [1.16.1.jar:?]
	at aoq.a(SourceFile:511) [1.16.1.jar:?]
	at bpd.d(SourceFile:256) [1.16.1.jar:?]
	at eei.a(SourceFile:22) [1.16.1.jar:?]
	at eei.a(SourceFile:12) [1.16.1.jar:?]
	at edw.a(SourceFile:107) [1.16.1.jar:?]
	at edw.b(SourceFile:96) [1.16.1.jar:?]
	at edw$$Lambda$4829/1124075978.run(Unknown Source) [1.16.1.jar:?]
	at edw.a(SourceFile:128) [1.16.1.jar:?]
	at edw.a(SourceFile:96) [1.16.1.jar:?]
	at ebx.a(SourceFile:1240) [1.16.1.jar:?]
	at ebs.a(SourceFile:717) [1.16.1.jar:?]
	at ebs.a(SourceFile:540) [1.16.1.jar:?]
	at dlx.e(SourceFile:1021) [1.16.1.jar:?]
	at dlx.e(SourceFile:654) [1.16.1.jar:?]
	at net.minecraft.client.main.Main.main(SourceFile:215) [1.16.1.jar:?]
Caused by: java.lang.ClassCastException: dym cannot be cast to zd
	at bbr.a(SourceFile:214) ~[1.16.1.jar:?]
	at aom.f(SourceFile:1636) ~[1.16.1.jar:?]
	... 20 more

MC-192362 has a detail analysis of the cause in code, using yarn names*

• Due to issues with Microsoft licensing, it's uncertain on whether we are legally permitted to use mojang names in this context.